The present invention relates to a vehicle driving aid apparatus which determines the wakefulness of a driver and issues an alarm to wake up the driver or to concentrate the driver on driving.
For the purpose of maintaining safety of driving, many proposals have been made on vehicle driving aid apparatus which determine the wakefulness of a driver using signals representing behaviors of a vehicle such as a steering angle, signals representing physiological changes in a driver, and so on and which issues an alarm using sounds or light to wake up a driver when it determines a reduction of the wakefulness of the driver.
For example, JP-A-10-315799 discloses a technique in which the wakefulness of a driver is determined based on the state of opening of the driver's eyes and in which, when a reduction of the wakefulness of the driver is determined, an alarm sound having a moving acoustic image is output to wake up the driver who has been at a low level of wakefulness, the wake-up sound lasting for a long time.
However, it is sometimes difficult to maintain the safety of driving sufficiently only by issuing an alarm to wake up the driver as in the technique disclosed in JP-A-10-315799.
Specifically, mis-steering is likely to occur due to a mis-judgment or operational delay of a driver during the time required for the driver to recover from a state at a low level of wakefulness to a wakeful state, and such mis-steering can cause a significant deviation of the vehicle from the driving lane. In particular, when the acoustic image of an alarm sound is moved as described above, the driver's consciousness may concentrate on the moving direction of the acoustic image at the instant when the driver recovers from the state at a low level of wakefulness, and the alarm sound can induce mis-steering rather than prevent mis-steering of the driver. It is therefore necessary to take sufficient countermeasures to a deviation from a driving lane and so on.